Mark Hengst

When a leading scientific researcher is killed by poisoning, Patrick Jane takes a personal interest in the case when he learns the prime suspect is the victim's wife - and Jane's former psychiatrist.

The pressure on Firehouse 51 is at an all-time high as the internal affairs investigation into the handling of a recent fire picks up steam. Just when it appears that game-changing evidence comes to light that would serve to bail out Chief Boden, new twists emerge that put his head right back on the chopping block.

Chief Boden (Eamonn Walker) confronts Maddox (guest star Mark Hengst), believing he is the hand behind Serena's (guest star Ilfenesh Hadera) accusations intended to skew Boden's credibility from the approaching trial. Severide (Taylor Kinney) reaches out to Jamie (guest star Rachel Nichols), Maddox's lawyer, in an effort to help out and Capt. Patterson.

Members of Firehouse 51 are less than thrilled when Captain Patterson (guest star Brian White) steps in as replacement for Chief Boden (Eamonn Walker) while he deals with clearing his good name. Severide (Taylor Kinney) learns of the potential whereabouts of Serena (guest star Ilfenesh Hadera.)

Jane and Maura find a man who died in a bathtub full of ice; while trying to stay cool during a heatwave, Angela discovers a spicy tea that brings unexpected romantic consequences.

On Valentine's Day, Mac and the team investigate three tales of love gone wrong.